Light emitting diodes are small dies with a size of approximate 0.3 mm which can only be clearly observed with a microscope. As shown in FIG. 6, wherein the general feature of an LED die is illustrated, the illumination areas of the LED are generated around a P-N junction 61 thereof and a-surface 62 which faces upward or outward. A connecting pad 63 is disposed on the surface 62 for electrical connection with a power source. To have all the light generated by the LED projected toward a same orientation, i.e., toward the upward or outward surface 62, it is desirable to provide a bowl-shaped reflector which comprises a recess having a reflecting surface, preferably a paraboloid, to surround the LED die. The reflecting surface is an essential element of an LED display in the point of view of projecting light in a given direction.
The LED lamp which is currently available in the market comprises a pair of metallic leads 71 and 72 as the connecting and supporting base thereof, as shown in FIG. 7. On one 71 of the frames, a bowl-shaped recess defining a reflecting surface 73 is formed. The LED die is placed on the bottom of the bowl-shaped reflecting surface 73. FIG. 8 is a partial cross-sectional view in a larger scale than FIG. 7, showing a portion of the lead on which the reflecting surface is formed. The location designated by the reference numeral 74 is where the LED die is placed. There is also a conductive wire 75 connecting between the LED die 74 and the other lead 72.
For a dot matrix LED display constituted by a number of LED dies, the arrangement is shown in FIG. 9 which comprises an upper cover 91 made of a plastic material having a plurality of smooth bowl-shaped recessed through holes 911 with a concave surface 912 respectively. The LED dies are disposed on the positions, indicated by the reference numbers 92, of the printed circuit board 93 which are respectively responsive to the bottoms of the bowl-shaped recessed through holes 911. When the upper cover 91 is assembled with the printed circuit board 93, each of the LED dies will protrude from the bottom of each of the bowl-shaped recessed through hole 911 and the concave surface 912 of the hole 911 will surround the LED die to serve as a reflection surface thereof.
One of the disadvantages of the above-discussed prior art LED lighting devices is that since the LED dies are disposed on the positions corresponding to the bottoms of the recessed through holes, the projection of the light emitted from the dies will be limited to the lower portion of the reflection surfaces 912 of the holes 911. This provides a less efficient light projection and thus making the LED device less illuminating. Therefore, the bowl-shaped reflection surfaces in the above-discuss cases fail to perform optimum functions.
Another commercially available LED display is constructed by directly soldering LED lamps as those 7 in FIG. 7 on a print circuit board 100 in the form of a matrix, as shown in FIG. 10. This arrangement is to replace the optically less efficient plastic reflecting surface of the conventional dot matrix LED displays as shown in FIG. 9 with the optically more efficient metallic reflecting surface of the LED lamps. The manufacturing process thereof, however, is much more complicated. Human labor is required to fix the LED lamps on the PCB one by one. Further, due to the interference of the electronic elements, such as integrated circuit chips, mounted on the same printed circuit board, the dipping soldering process may be incomplete. Besides, since the disposition of the LED lamps on the printed circuit is done by human labor, the disposition orientation of the LED lamps may not be consistent with each other so as to effect the illuminating quality thereof. Also, since only the LED lamp itself is encased by a resin enclosure, the soldering portion thereof with the printed circuit board is not enclosed and is not water-proof.
It is therefore desirable to provide an LED lamp lighting structure which can project light more efficiently than the prior art and it is also desirable to provide an dot matrix LED display which is constructed by applying the same optical principle so that a better illuminating efficiency can be achieved.